VELOCITY OF REACTION 189 



maximum, and the velocity of reaction can begin to obey the 

 logarithmic law. It is hence only in dilute solutions (com- 

 pared to the amount of enzyme) that the amount of sugar con- 

 verted per unit time can be proportional to the amount present, 

 and this condition Adrian Brown found to be experimentally 

 realised. 



It is clear that this conception of A. Brown's is really coincident 

 with that of Arrhenius of the " active mass." 



The catalysis of starch by the action of diastase was next studied 

 by Horace Brown and Glendinning, who showed that the velocity 

 curve in this case also is at first represented closely by a straight 

 line, but later approximates to the logarithmic curve. These authors 

 also assume a combination between the enzyme and its substratum, 

 and that at first the concentration of enzyme is small compared to 

 that of the substratum. As before, as long as the amount of sub- 

 stratum is large, the amount of combined substratum and enzyme 

 will remain constant, the amount therefore converted in unit time 

 will remain constant, and the velocity curve will be a straight line. 

 Later, when the concentration of substratum falls off, the amount 

 in combination will begin to vary directly as the concentration at 

 any moment of the substratum and the logarithmic law will begin 

 to hold. 



An extensive series of observations on the hydrolysis of various 

 proteids, chiefly caseinogen and gelatin, by the action of trypsin 

 has been published by Bayliss. The method used was that of 

 measuring the increase in electrical conductivity, and it appears 

 from his statements to be both convenient to carry out experiment- 

 ally and to give reliable results. 



With regard to the course of the reaction, Bayliss found that 

 the curve representing quantity converted and time fell off con- 

 tinuously and rapidly throughout the experiment from the loga- 

 rithmic curve, the velocity constant decreasing in value to the 

 end. The form of the curve (which tends to become asymptotic 

 to the base-line) shows that the velocity of reaction tends to 

 become zero that is to say, that there is an equilibrium point with 

 the reaction incomplete. It was found that the position of this 

 point of rest altered with the same factors as have already been 

 described as causing an alteration in Tammann's experiments 

 viz., alteration of concentration of substratum; alteration of con- 

 centration of enzyme; alteration of concentration of the system 



